Environmental Friend And

ENVIRONMENTAL FRIEND AND
RATIONAL USE OF ENERGY WITH HEAT PUMPS

Ferenc KOMLÓS
Chief Designer Building Engineer
H-2330 Dunaharaszti, Klapka György utca 41/1., e-mail:

Abstract

The heat pumps are the most efficient technological tools in energy saving and in reducing carbon dioxide emission. As a matter of course reducing the energy consumption of buildings is necessary also because of the need for improving the energy balance of Hungary and for reducing urban (community) air pollution.Related to the technology of today – and of tomorrow – it is also important to mention, that in addition to the heat source also the operation of the heat pump and the input energy can originate from renewable (inexhaustibly available) energy sources.

Motto:

“When you ask me, if we are late, if the destruction of the nature caused by the mankind is irreversible, then my answer is: we are not late. Until the will exists, it is never too late. And if people want to do something together, they do it in deed reaching so the goal whatever it is.”

(Ede Teller)

By a more successful utilisation of those described above we can make mainly our heating / cooling bills cheaper, can reduce the consumption of the so called traditional energy sources (also for the reason that traditional energy sources will run out and will be more and more expensive) and can reduce the pollution of our environment. Thus heat pumps have a growing role in the different application fields including the use and utilisation of waste heat (Fig. 1.).

Fig. 1. Primary energetic efficiency degree of different heat generation methods.

(Primary energy: collective noun of primary energy sources being available and can be used for energy transformation)

Source:Joós Lajos: Energiamegtakarítás a háztartások földgázfelhasználásában. Magyar Épületgépészet, XLI. évf. 2002/4. szám

Knowledge of the application possibilities of heat pumps is a basic precondition of their use. They can only be economically and safely used if the system related conditions of the heat pump cycle are harmonised with the application conditions. It is proposable to investigate the widespread application possibilities of heat pumps in case of new technologies, investments and in case of modernisation and reconstruction of existing facilities. For example if in case of a warm water central heating system the greater heating surface will be dimensioned, the less can be the temperature of the forward flowing heating water and the higher is the achievable COP (Coefficient of Performance) and its power factor (), the calculation of which can be performed with the following equation:

COP= [kW/kW] = heat flow being utilisable for heating / power input for operation

Factor COP and are also proportional with the fraction T/(T–T0), so its actual value is determined by the temperature of the heat source (~T0) and of the heating (~T) and by the temporal trend of both factors. Heat pump systems with simultaneous heating and cooling can obviously be classified to the technologies with outstanding motivation.

The “László Heller Scheme” [1]: With regard to the job generation; to the popularisation of renewable energies; to energy saving; to the enhancement of energy efficiency; to those contained by the energy policy and energy strategy of the European Union; to the unavoidable need of air conditioning, heating and cooling; to the increase of our exportability; to the decrease of our energy independence and to the impacts on the sustainable development I propose to the decision makers to include the Heller László Programme into the National Development Plan II. The essence of this programme is a long-term replacement of the natural gas fuelled boilers and electric boilers by heat pumps of different design and operating mode fulfilling mass needs. These heat pumps should be manufactured in Hungary, they should be designed, installed and maintained by Hungarian manpower in locations mainly in Hungary and in Middle-Eastern Europe. Their further development would be realised in Hungary as well.

In addition to the three “great renewable sources”: solar, wind and water energy in the future the thermal energy of the (environmental) air and soil can have a determinant role too as heat accumulators of solar energy with unlimited measures. These renewable energy sources in our environment can be reasonably utilised by heat pumps as utilisation tools[2].

There were no significant changes in the radiation of the Sun long ago and there are no changes expected for a long time in the future (the solar constant is measured for about 100years and since 1979 measurements with high accuracy are made; solar constant is the numerical value indicating the amount of energy reaching the upper boundary of the atmosphere for surface unit perpendicular to the propagation direction of the radiation for time unit from an average Earth-Sun distance). Solar constant varies for day to day, week to week, month to month, the changes are nearly periodic and their peak to peak difference does not exceed 0,5 %. The value of the solar constant falls between 1364 and 1372 W/m2 depending on the measuring device. Utilisation possibilities of solar radiation depend on the location of a given country on the Earth. Value of the average radiation reaching the Earth’s surface is about 177 W/m2 and 1200–1450 kWh/m2 of this can be utilised as an annual average. In a year 300–400 EJ (1 EJ “exajoule” =1018joule) solar radiation reaches the surface of Hungary [3].

Let us see what happens with the energy radiated by the Sun onto the Earth? The change in radiation energy does not exceed3 % of Earth’s average and local differences are below 10%. Thermal radiation reaching the Earth’s surface warms up the surface and the beams mirrored back by it heats up the air near to the surface, i.e. the so called turbulent boundary layer as well. The actual material and energy transfer takes place in this layer, this layer is called also as Prandtl layer. Absorbed energy is the main source of heating up of the air. The air is heated up by heat radiation absorbed by the soil and water and having been transformed into heat radiation with longer wave length. Average air temperature of the atmosphere near to the surface is now around 15°C. The annual average temperature in Hungary varies between 8–11°C, average value of the temperature gradient is 0,65°C/100 m. Highest values are characteristic for the South-eastern part and the lowest values to the North-eastern part of Hungary. The air of the atmosphere is a heat accumulator of the solar energy with endless measures and environmental temperature level unrestrictedly available everywhere. The temperature increases also in Hungary, e.g. in Budapest the annual average temperature was 9,6°C between 1871 and 1900; 11,0°C between 1901 and 1950; 11,2°C between 1961 and 1990. The said renewable energy source can be utilised e.g. with the help of air-water heat pumps not only for hot water production, but also for heating. Even an outer air mass with the temperature of 2°C (275 K) has a significant amount of accumulated heat, as heat capacity increases from –273,15°C (0 K) proportionally with the temperature (base point of the Kelvin scale is the theoretical boundary of termination of the thermal movement, temperature differences on both scales are the same) [4].

The outer air temperature during heating periods increases in the towns (urban built in areas results so called heat islands mainly because of the energy production and less air movement), e.g. in Budapest the mean temperature in January is 3–4°C higher than that of the areas outside from towns. For the changing outer air temperature heat pumps are generally installed and combined with an other heat generator (boiler) for heating tasks, because with decreasing air temperature the economic efficiency of heat extraction decreases too. From economic aspects it is essential, that the heat source has the highest possible temperature, can be easily and cheaply utilised and have sufficient energy yield. Air near to the surface as heat source is available everywhere and in unlimited quantity. However its temperature is the lowest when the need for heating is the highest. Heat pump operation is economically efficient if energy saving exceeds the excess investments costs for the heat pump. Especially efficient are heat pumps performing contemporary heating and cooling. Air-water type heat pumps are those ensuring economically efficient heating during a significant period of the heating season and are widely used e.g. in Germany; or as an other example it can be mentioned, that 59,9 % of the heat pumps distributed by HOVAL in Switzerland are air-water type heat pumps (reference: presentation of Mr. AdolfHeeb, Hovalwerk AG in Budapest in 2004).

In case of these heat pumps the compressor is not driven by an electric motor, but by an internal combustion engine (e.g. engines of Toyota Group) with infinitely variable speed between 10 and 100 %. Heat source of air conditioning devices with gas engines is in general the air from the environment. Outer air as a heat source has the benefit being available everywhere independently from building in, also in towns to an unlimited extent. It is a heat source (renewable energy) that can be used also in locations, where for lack of space no earth probe can be installed. If the temperature of the outer air drops significantly, e.g. from +7°C to –10°C, the power of air conditioning device with gas engine decreases only by 5 %, while that of electric heat pumps equipped also with a compressor decreases by 45 % [reference: AISIN TOYOTA Group Gaswärmepumpen CD 2005, Open air units have low noise and low harmful material emission. By mounting a freon-water module an air-processing equipment, fan-coil devices and e.g. wall heating resp. wall cooling systems can be attached to the air conditioning device with gas engine[4].

Air conditioning devices with gas engine and heat pump are suitable for air conditioning either in winter or in summer. Costs of the cooling energy produced by electrically operated air conditioners are now more than twice as high as the cooling energy costs of air conditioners with natural gas fuelled engines (electric energy is a secondary energy and natural gas is a primary energy source). During the expansion of heat pumps operated by natural gas energy the question will be raised many times: boiler and/or heat pump? Using heat pumps means a great technical challenge. In a given case individual needs are to be met; optimum solution is to be found for the given location, for the energy source being available, for the needs of the building and of the investor. If the decision is made for the use of a heat pump, it has to be preceded by economic calculations. These have to contain the comparison of investment, energy and operation costs of the variants being feasible. Economic efficiency is favourably influenced, if the heat pump is used for heating during cold periods and for cooling in warm periods (Fig. 2-3.).

Fig. 2. The Principles and Sankey-energy flow of a compressor driven heat pump.

Fig. 3. Heat pump system with compressor, combined with solar collector.

Source: DANFOSS Co.

The Earth’s crust contains everywhere soil heat (thermal energy). The reason of this fact is, that the temperature of the material below the surface is determined by two heat sources, by the radiation of the Sun and by the internal heat of the Earth. The former penetrates inward from the surface and later comes outward from the inside of the Earth. (The other great heat source is the inside of the Earth.) Heat of the Earth flows continuously to the surface of the Earth by convection, conduction and radiation. Soil heat is an internal energy accumulated by the masses of high temperature of the Earth’s crust, mantle and the core. Average value of heat flow that can be measured on the surface is between 0,06 and 0,07 W/m2, within the Carpathian Basin it has an average value of 0,10 W/m2, in Hungary the average Earth’s heat flow is 0,09W/m2.Average heat flow on the lowland of Hungary is 0,10 W/m2 being about twice as high as world average [4]. In solid soil heat propagates by molecular heat convection being a rather low phenomenon, in water material flow is an intense energy transporting process. It can be seen from the above that the amount of the heat on Earth’s surface is only a fraction of the heat originating from the Sun, but it is significant from the aspect of the underground waters. In the direction to the Earth’s centre the increase of the temperature related to length unit is called geothermal gradient (Fig. 4-5.).

Fig. 4. Heat pump systemused geothermal energy, combined with a peak-boiler.

Fig. 5. Heat pump system to greenhouses, combined with a wind turbine.

The figure on the left shows the evaporator of the heat pump and the engine-house at a close. The figure in the middle shows the green-house and the wind turbine behind it (during periods of calm the compressor of the heat pump is driven by mains current). In the figure on the right heat supply of the green-house of 600 m2 by an air-water heat pump can be seen. Ireland 1986.

Source: No 81. European Community Demonstration projects for energy saving and alternative energy sources.

A rapid development has begun in this field never experienced before. There are intense researches and developments, but for a competitiveness significant support is required. For the breakthrough expected for the near future we have to prepare ourselves in the field of technology too.

Potentialities of our country, namely its solar and thermal energy reserves and its biomass energy potentials in a wide sense and its high level intellectual capital are favourable to the renewable energy based technologies and these potentialities belong to our national treasure, these are the clues to a cleaner environment. During a period similar to that of the natural gas programme also these technologies can favourably emerge on a complex way and can contribute to the prosperity of our environment industry and sanitary services.

Related to the technologies of today – and of tomorrow – it is important to remark, that not only the hat source, but also the operation of the heat pump, i.e. the input energy can originate from renewable (inexhaustibly available) energy sources, this being clearly shown in Table 1.

Table 1. Main heat sources of heat pumps and driving solutions of its compressor motors

RENEWABLE ENERGY SOURCESAND CARRIERS / DRIVING of the COMPRESSOR
Sun
including direct utilisation and through solar power plant of the heat content of the warmed up atmosphere and surface of the Earth (ambient air, soil, surface waters, subsoil water) and of radiated energy / Electric motor
Wind
including its utilisation through wind generators (conversion of kinetic energy)
Water
including its utilisation through water power plants (conversion of potential and/or kinetic energy)
Biomass
(solid, liquid and gas phase fuels) including its utilisation through electric power plants
Soil heat
(geothermal energy: heat reserve of the inside of the Earth originating mainly from the decomposition heat of radioactive elements with long half-period in the Earth’s crust and mantle) including utilisation of heat accumulated in thermal waters (waters under the surface) and in rocks and its utilisation through geothermal power plants
Biomass
including the utilisation of produced liquid or gas phase fuels (bioethanol, biodiesel, biogas, biomethanol, bio-dimethyl-ether, bio-ETBE*, Bio-MTBE**, synthetic bio fuels, biohydrogen, pure vegetable oil) /
Internal combustion engine

* bio-ETBE (ethyl-tercier-butil-ether): ethyl-tercier-butil-ether produced on bioethanol basis having a biofuel content of 47 % vol.

** bio-MTBE (methyl-tercier-butil-ether): fuel produced on biomethanol basis having a biofuel content of 36 % vol.

References

[1] F. Komlós:Hogyan lehet csökkenteni a szén-monoxid-mérgezések számát és a Heller program (The Way of Decreasing the Number of Carbon Monoxide Poisoning and the “Heller-programme”).
18. Fűtés- és Légtechnikai Konferencia, Budapest, Hungary, 2006. 05. 10–12. (Association partners: EU Concerted Action Working Group, “Országos Lakás- és Építésügyi Hivatal”, REHVA). On CD.

[2] F. Komlós: Természetesen hőszivattyú (Heat pump, naturally).
Magyar Energetika, XIII, 2005/4, pp. 34–36.

[3] F. Komlós: A környezetbarát hőszivattyús fűtéstechnika (Environment–friend Heat Pump Heating Technology). Elektrotechnika, IIC, 2005/9, pp. 237–240.

[4] F. Komlós: Hőszivattyúk és a megújuló energiaforrások épületgépészeti alkalmazása (Heat pumps and renewable energy sources use in HVAC applications).
Építésügyi Szemle, XLVII, 2005/3, pp. 89–96.